I've got a CRT here with bad fungus between the tube and safety glass layer. There are various videos on tut'net that show how to prise the protective glass off the screen using a heat gun and scraper, then clean and reassemble. Yet this screen is a bit different as it has a mounting frame that wraps around the front of the tube, preventing me from removing the safety glass and the glue underneath.

The frame appears to have been bonded to the screen using potting compound.

It looks black but under the coating it's white and quite hard. I haven't tried to heat it other than to stab it with an iron at 350C and it hasn't really reacted.

Does anyone know what it might be, and whether the bezel can be safely removed in one piece?

I have to say, I'm not too sure about this. I read on Herb Johnson's web site that the frame is a part of the CRT's implosion protection and shouldn't be removed. I might be able to grind the curved bezel part off the frame, though, or break the safety glass (carefully) and remove it piecemeal?